Rc Time Constant
Calculator
Results
- Time constant (s)
- 1
- Time constant (ms)
- 1,000
- Voltage after one time constant (V)
- 7.585446
- Time to about 99% (s)
- 5
Electrical results
| Time constant (s) | 1 |
| Time constant (ms) | 1,000 |
| Voltage after one time constant (V) | 7.585446 |
| Time to about 99% (s) | 5 |
formula-map diagram
- Time constant (s)
- 1
- Time constant (ms)
- 1,000
- Voltage after one time constant (V)
- 7.585446
- Time to about 99% (s)
- 5
Electrical relationship
Formula
τ = R × C= 1
Note
This is a simplified model: it applies the textbook relationship to the numbers you entered and assumes ideal components, steady-state sinusoidal conditions, balanced loads and copper resistivity of 0.0172 Ω·mm²/m at 20 °C. It ignores component tolerances, temperature drift, skin effect, harmonics, inrush, transformer and battery losses, and it is not a substitute for the wiring code that applies where you are. Have any installation sized and verified by a licensed electrician or engineer.
More in Electrical engineering
See all →Frequently asked questions
What does the RC time constant actually represent?+
Tau = R x C is the time it takes a charging or discharging capacitor to reach about 63.2% of the way to its final voltage. It's a natural unit for measuring how fast an RC circuit responds.
How long does it take for a capacitor to fully charge?+
In theory, a capacitor never reaches 100% charge — it approaches it exponentially forever. In practice, it's considered fully charged after about 5 time constants (5RC), at which point it's over 99% of the way there.
Why do larger resistor or capacitor values slow down the circuit?+
A larger resistor limits the charging current more, and a larger capacitor needs more charge to reach the same voltage — both effects independently increase the time needed, which is why they multiply together in tau = RC.
What's a practical use of the RC time constant?+
It's used to design timing circuits, filters, and debounce circuits — for example, choosing R and C values to create a specific delay before a signal crosses a threshold, or to set the cutoff frequency of a simple RC filter.
Does the time constant depend on the applied voltage?+
No, tau = RC depends only on the resistance and capacitance values, not on the voltage level. A circuit charged from 5V or 50V reaches 63.2% of its respective final value in exactly the same amount of time.